Asymmetry of Model Bin Wall Loads and Lateral Pressure Induced from Two and Three-Dimensional Obstructions Attached to the Wall

Abstract

An obstruction attached to the wall of a bin due to cohesive, moldy grain has been reported as asource of failure in steel bins. These obstructions were modeled using eccentric structuralmembers fastened to the wall. A study was conducted to estimate the effect of a two- (plane) andthree-dimensional (block) obstructions attached to the corrugated wall in a flat floor model binwhere the lateral wall pressure and vertical wall load were measured. The bin was 1.83 m indiameter and 5.75 m high filled with soft red winter wheat to a depth of 5.0 m (height-to-diameterratio h/d of 2.75). Geometrical imperfections in the bin and imperfect centric loading andunloading of the bin were observed to produce significant unsymmetrical states of stress evenunder nearly symmetrical conditions of operation. The plane obstruction had the form of anannulus segment of 60 in circumferential extension and a width of 0.154 m (surface area of 7.2%of the bin floor area). A three-dimensional obstruction was shaped as a block with two basesidentical as the plane obstruction and a height of 0.5 m. The plane obstruction and upper base ofblock obstruction were attached to the wall at h/d ratios of 1.26, 0.81 and 0.38. Lateral pressurewas determined using two pressure cells attached above and below the obstruction. In thefollowing test the pressure determination was taken with the obstruction removed from the bin.Simultaneously vertical wall and floor loads were measured that allowed for evaluation of wallload asymmetry. Even in conditions of near symmetry during centric loading, wall overturningmoments of approximately 1 kNm were observed. Attachment of an obstruction resulted in anincreased moment. The highest wall moment of 2.7 kNm was found at the end of filling the binwith the block attached at h/d of 0.38, the moment with a plane obstruction in the same conditionwas measured as 2.1 kNm. The maximum moment measured in this bin for eccentric unloadingwith no obstruction was 3.5 kNm. For higher locations of the obstruction on the wall, wallmoments were found approximately 50% of the value at h/d of 0.38. Lateral pressure distributionalong the bin height during filling was found in good agreement with Janssen's equation. At theonset of discharge a sudden increase in lateral pressure was observed. Without an obstructionattached to the wall a maximum pressure increase of 2.5 times the static pressure was observed.Dynamic pressure increases above the obstruction were a maximum of four times the staticpressure. Conversely dynamic pressure increases below the obstruction were lower than withoutthe obstruction attached. The data collected indicated that there are considerable additional loadsplaced on a bin due to obstructions that may form during storage that are not considered in thedesign codes.